This invention relates to a method of controlling exhaust gas recirculation for an internal combustion engine, and more particularly to a method of this kind including detecting failure in an exhaust gas recirculation system of the engine.
Conventionally, there have been proposed the following manners of detecting failure in an exhaust gas recirculation system:
1) According to Japanese Provisional Patent Publication (Kokai) No. 55-123345, it is determined that there is failure in the exhaust gas recirculation system when the difference between a desired value of opening of a control valve which controls an amount of exhaust gas recirculation and an actually detected value of same has become larger than a predetermined value.
(2) According to Japanese Provisional Patent Publication (Kokai) No. 60-11665 and Japanese Patent Publication (Kokoku) No. 63-9103, it is determined that there is failure in the system when the above difference has continued to be larger than the predetermined value over a predetermined time period or longer.
(3) According to Japanese Provisional Patent Publication (Kokai) No. 61-81567, it is determined that there is failure in the system when the relationship in magnitude between a desired value of opening of the control valve and an actually detected value of same has remained uninverted over a predetermined time period or longer.
In general, when the engine is accelerating or decelerating, the desired value of opening of the control valve is largely changed, and there is a time lag in the following-up of the actual value of same, which results in an increased difference between the desired value of opening and the actually detected value of same. Therefore, according to the above manners (1) and (2), there can be a case in which the difference goes beyond the above-mentioned predetermined value when the engine is accelerating or decelerating, and hence failure in the system is erroneously detected. If the predetermined value is set to a larger value in order to prevent such an erroneous detection of failure, there arises an inconvenience that failure cannot be detected except when the control valve continues to be fully opened or closed.
Further, according to the above manner (3), if the desired value and the actually detected value are nearly equal to each other and stable, and hence the relationship in magnitude between the two values remains uninverted for a long time period, when the engine is in a steady operating condition, it is erroneously determined that there is failure in the exhaust gas recirculation system although actually the system is normally functioning.